**5. AC/DC and hydro microgrid**

Microgrids are the most prominent grids to extract various types of distributed renewable energy sources with the distribution grid. The distribution utility side grids are AC grids, since today electrical loads are connected with power electronic devices, and since most of the renewable energy sources are DC power supply, now the DC microgrids concepts are gaining more attraction. The most common

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**Figure 7.** *Hybrid microgrid.*

*Microgrid*

*DOI: http://dx.doi.org/10.5772/intechopen.88812*

several technical challenges.

grids are AC microgrids which uses standard protection technique's to manage disturbances. But the distributed generation sources for microgrid comprising of solar cell arrays and fuel cells are DC power which needs to convert to AC power through power electronic device. This DC power source in the microgrid is connected to the power supply through inverter to the utility grid. The AC power on the utility side is converted back to DC for some of the latest electrical loads such as UPS batteries, DC lighting loads, DC motor drives, and hybrid electric vehicles. Due to multiple conversions, AC microgrid becomes inefficient due to more power losses due to multiple conversions. Apart from that maintain synchronism, stability issues and reactive power requirements are the challenges faced by AC microgrids. Due to this reason, DC microgrids are emerging as alternate grids. But the diesel generator, small microturbines connected synchronous generator, and wind energy generators are required to connect with AC/DC converter to distribution side grid. Due to multiple conversions, DC microgrid also becomes inefficient due to more power losses due to multiple conversions. The reason for this problem is now-a-days electrical load becomes mix of both AC and DC power. It leads AC/DC grids to less efficient operation. The best solution to avoid this multiple conversion energy losses is hybrid AC/DC microgrid. The hybrid AC/DC microgrid is formed with an objective to minimize the conversion losses to make the microgrid more efficient as shown in **Figure 7**. But the implementation of hybrid of AC/DC grid required

Hybrid microgrid comprises both AC and DC sources as shown in **Figure 7**. The respective AC and DC sources are connected to the corresponding AC and DC networks. The AC bus and DC bus are linked together with three phase converters and the transformers. The AC bus of hybrid grid is tied with distribution grid with transformer and circuit breaker. The successful operations of hybrid microgrid are based on power conditioning converters. The converters are classified based on their input and output power supply. The converters used in hybrid microgrids are rectifier, inverter, buck/boost converter, and transformers. Among these converters, inverters and boost converters need more attention than conventional converters in the microgrid. Because the boost converter is very much required to interface low voltage PV arrays into the microgrid and then converted into AC power through inverter to feed the loads. **Figure 8** shows how the converters are theoretically
